Sucrose has heretofore been widely used in confectionary and food by virtue of its excellent characteristics, such as good sweetness, body, taste and crystallinity. Sucrose, however constitutes a substrate for dextransucrase produced by intraoral microorganisms, and, as a result, consecutive intake of sucrose leads to formation of large amounts of insoluble dextran in the mouth. Thereby formation of dental plaque is accelerated. Therefore sucrose is said to possess cariogenicity. Recently there has been a trend to reduce the calorie intake for prevention of obesity and a low-calorie sweet material instead of a high-calorie one, such as sucrose, has been demanded.
For this reason many suggestions have been made as to find a sweet material for replacing sucrose, such as the artifical sweeteners saccharin, cyclamate, aspartame, sorbitol and many others.
Such alternative sweeteners are widely used but also possess several disadvantages, such as a bitter tang or aftertaste. Furthermore, some of the artificial sweeteners are suspected to be carcinogenic.
These disadvantages, especially the suspicion of being carcinogenic - a recurrent subject in the public debate have made consumers reluctant to use products containing any type of artificial sweetener.
It is known that the Dahlia tubers contain a polysaccharide known as inulin. According to Merck Index, 10th edition, Merck & Co. Inc., Rahway, N.J., U S A, 1983, p 725, Index no. 4872, it has the formula GF.sub.n with n being of an average value of approx. 37. The preparation of inulin from dahlia tubers is disclosed in U.S. Pat. No. 4,285,735.
It is also known that chicory roots and Jerusalem artichoke tubers contain corresponding polysaccharides or oligosaccharides with the general formula GF.sub.n. The value of n varies depending on the raw plant material in question, cf. e.g. S. E. Fleming et al., Preparation of high-fructose syrup from the tuber of the Jerusalem artichoke (Helianthus tuberosus L.). CRC Crit. Rev. Food Sci. Nutr., 11, 1.23, 1979, U.S. Pat. No. 4,613,377 and EP patent application no. 0 201 676/A2.
The interest in these polysaccharides and oligosaccharides in form of inulin or inulin-like compounds (inulides) has until now been directed to the large content of fructose moities in said compounds. They are thus a useful source for the preparation of fructose, especially with regard to using the fructose as nutrient replenisher and sweetener.
EP patent application 0 201 676 discloses a method for preparing a low-glucose cleavage product from plant parts said cleavage product comprising inulin-like oligo- or polysaccharides. According to this method the extracted oligo- or polysaccharides are subjected to treatment with the enzyme inulinase in order to decompose them to fructose and fructose-oligomers.
U.S. Pat. No. 4,613,377 discloses a method where the inulin-like oligosaccharides obtained from Jerusalem artichoke tubers or chicory roots, are subjected to partial or substantially complete hydrolysis.
Further prior art disclosing the general state of the art comprises the following.
GB-PS no. 1.405.987 discloses the preparation of a mixture of fructose and glucose, i.e. invert sugar, by crystallization.
U.S. Pat. No. 2,555,356 discloses the preparation of inulin from Jerusalem artichoke. The inulin obtained is used as a substitute for starch and for the preparation of levulose and alcohol.
U.S. Pat. No. 4,138,272 discloses a method for the preparation of fructose from xerophyte plants, for example Agave.
DE-OS 3.211.776 discloses a method for obtaining juice from Jerusalem artichoke to be used for the preparation of hydrocarbons, for example acetone butanol.
Derwent's abstract no. 87 305.414/43, SU patent application 306.061 (SU.PS 1.300.032) discloses the preparation of fructose from Jerusalem artichoke.
Non-patent literature concerning the analyses of "inulin" from Jerusalem artichoke is mentioned in
Chemical Abstracts (CA), vol. 26, (1932), p. 5355, Food Ind. 4, 66-9(1932); PA1 CA, vol. 29, (1935), p. 8387, Sovet. Sakhar 1935, No. 1, 4-47; PA1 CA, vol. 50, (1956), col. 13152 g Trudy Komissii Anal. Khim., Akad. Nauk. S.S.S.R., Inst. Geokhim. i Anal. Khim. 6, 492-7(1955); PA1 CA, vol. 51, (1957), col. 9813 a, Zucker-Beih. 3, 86-94(1957); PA1 CA, col 53, (1959), col. 18189 c, Cukoripar 12, 126-9(1959). PA1 1. separation followed by adjusting the pH value by adding CO.sub.2 or phosphoric acid and subsequent separation, or PA1 2. adding CO.sub.2 or phosphoric acid and subsequent separation, i e the extract is only separated once. PA1 (a) the substantially cleaned tubers or roots are cut into cosettes, PA1 (b) the cosettes are subjected to extraction with water, PA1 (c) the extract, or juice, is treated in a suitable order one or more times by each of the following steps: PA1 (d) the juice from step (c) is subjected to ion exchange, PA1 (e) the juice from step (d) is optionally treated with active carbon, PA1 (f) the juice from step (e) is optionally concentrated by hyperfiltration, PA1 (g) the juice from step (d), (e) or (f) is evaporated to a syrup with a dry matter content of 91-96% by weight, PA1 (h) the syrup is dried and ground to a powder. PA1 (i) the syrup is distributed as a thin layer on a cooling surface with a temperature of below 0.degree. C., preferably between minus 10.degree. C. and 0.degree. C., whereby the syrup solidifies to a hard glass-like mass, PA1 (k) the hard glass-like mass formed in step (i) is scraped off the cooling surface in form of flakes, PA1 (l) the flakes are roughly ground and PA1 (m) the roughly ground flakes are dried at a temperature of below 60.degree. C. to a dry matter content of above 96% by weight, preferably above 97% by weight, PA1 (n) the temperature of the syrup is adjusted to a value below the boiling point of said syrup at atmospheric pressure, PA1 (o) the syrup is fed into a vacuum chamber, PA1 (p) the syrup is led through the vacuum chamber without any heat supply to the syrup, PA1 (q) the obtained dried or evaporated product is removed from the vacuum chamber through an air lock.
From the British patent applications nos. 2.072.679, 2.105.338 and 2.179.946 a low-calorie sweet material is known comprising a mixture of oligosaccharides with 1-4 molecules fructose bound to sucrose, i.e. a mixture of the oligosaccharides GF.sub.2, GF.sub.3, GF.sub.4 and GF.sub.5. The above mixture is prepared by stepwise synthesis from sucrose letting the enzyme fructosyl transferase act upon sucrose: ##STR1##
This synthesis is expensive and yields only small amounts of the oligosaccharides GF.sub.4 and GF.sub.5. Moreover, the above reaction 1) results in the production of an excess of glucose. The known sweet material is available under the name "Neosugar", both in form of a syrup and in powder form. "Neosugar" does not possess the detrimental effects of sucrose or alternative artificial sweeteners mentioned above, its preparation is, however, too expensive to allow wide use thereof. Furthermore, consumers are probably reluctant to use the product if presented as a chemically modified product.
There is thus still a need for a method allowing the preparation of a sweetener on the basis of a natural product without the detrimental effects of sucrose and conventional alternative sweeteners, said method being inexpensive and not involving chemical modification of the desired natural components in the starting materials.